1. Field of the Invention
The present invention relates generally to a remote access device having a low-frequency inductive coil antenna with multiple inductors and, more particularly, to a remote keyless entry access device located within a hand held transmitter, the device having a low-frequency inductive coil antenna with multiple inductors.
2. Background Art
It is well known in the automotive industry to provide for remote access devices, such as remote keyless entry (RKE) to a vehicle through the use of a remote hand held transmitter, which is commonly referred to as a “fob.” Currently available RKE fobs may be separate units, or may be part of an ignition key head, which may additionally include a key-head transponder for use in a vehicle immobilization system. Such RKE fobs generally utilize an antenna to transmit radio frequency (RF) signals to a vehicle in order to lock or unlock vehicle doors, open or close a vehicle sliding door, unlock a vehicle trunk, activate internal and/or external vehicle lights, activate a “panic” alarm, and/or perform a variety of other functions. Remote access systems using such RKE fobs may employ on-off keying (OOK) or amplitude shift keying (ASK) modulation schemes for the RF signals.
Examples of such RKE systems are described in U.S. Pat. No. 6,094,131 to Chen et al., U.S. Pat. No. 5,933,074 to Settles et al., and U.S. Pat. No. 5,486,793 to Hill. In particular, U.S. Pat. No. 6,094,131 discloses a keyless lock device for a car. The device includes a master control unit installed in a car and a remote controller carried by a user. The master control unit has a processing unit connected to a centralized locking control unit of the car to lock and unlock the door of the car in response to signals received from the remote controller.
U.S. Pat. No. 5,933,074 discloses a remote control transmitter broadcasting RF signals conveying plural information components. In the preferred embodiment thereof, the remote control transmitter operates in conjunction with an RF receiver installed in a vehicle to unlock the doors of the vehicle when a unique RF signal is broadcast within a defined range. The remote control transmitter also operates in conjunction with the RF receiver in the vehicle to actuate the horn of the vehicle when the same RF signal is broadcast outside the defined range.
U.S. Pat. No. 5,486,793 discloses a balanced RF oscillator and transmitter circuit. The circuit includes a pare of balanced oscillators for generating an enhanced power radiating output signal. The circuit may be used with an automotive vehicle remote keyless entry system for remotely controlling access to a vehicle in addition to controlling other vehicular functions such as alarm system features, trunk release, etc.
A number of other types of RKE systems, as well as devices that may be used in RKE systems are also known. Examples or such systems and/or devices are disclosed in U.S. Pat. No. 5,561,430 to Knebelkamp, U.S. Pat. No. 5,680,077 to Jonely et al., U.S. Pat. No. 5,811,885 to Griessbach, U.S. Pat. No. 5,920,234 to Hill, U.S. Pat. No. 5,923,300 to Mejia, U.S. Pat. No. 6,043,752 to Hisada et al., U.S. Pat. No. 6,084,317 to Wolfe et al., U.S. Pat. No. 6,091,343 to Dykema et al., U.S. Pat. No. 6,130,622 to Hussey et al., U.S. Pat. No. 6,154,102 to Weber, and U.S. Pat. No. 6,130,606 to Flick.
The RKE systems of the types described above may be characterized as active in nature, where a switch or pushbutton must be activated by a user in order to have a desired remote access function performed, such as locking or unlocking the vehicle doors. Alternatively, RKE systems may also be passive in nature, where no such switch or pushbutton activation by a user is required in order to perform a desired remote access function.
In that regard, an example of a passive RKE system is disclosed in U.S. Pat. No. 5,319,364 to Warakas et al. The passive keyless entry system described therein includes a beacon carried by an operator designed to automatically unlock the vehicle as the operator approaches the vehicle, without the need for operation of any switch or pushbutton by the operator. Similarly, the system is further designed to automatically lock the vehicle as the operator, carrying the beacon, moves away from the vehicle. In addition to the portable beacon carried by the operator, the system includes a receiver/controller located in the vehicle and an antenna connected to the receiver/controller for receiving a radio frequency encoded transmission from the beacon for locking or unlocking the vehicle.
It is also known to provide remote access devices for use in entry gate or garage door operating systems, as well as in tire pressure monitoring systems of the types well known to those of ordinary skill in the art. For example, in a garage door operating system, a remote transmitter, which may be a separate hand-held device or integrated into a vehicle, is designed to provide remote access to a garage door actuator, such as through the transmission of a radio frequency control signal.
In tire pressure monitoring systems, small remote transmitters located in the vehicle tires provide remote access to a receiver/controller in the vehicle. The remote transmitters transmit signals indicative of tire pressure and other information to the receiver/controller, which may then display such information to a vehicle operator. Alternatively, remote transceivers may be located in the vehicle tires to provide remote access to a receiver/controller in the vehicle through tire pressure information signals transmitted to the receiver/controller as well as through communication signals received by from the receiver/controller.
Current products using remote access technology, such as within an RKE fob, use as an antenna a single inductive coil. As is readily apparent to those of ordinary skill in the art, such an antenna is inherently optimized for a single plane of magnetic field transmission and/or reception. As a result, in the case of an RKE fob, depending upon the orientation of the RKE fob and/or its distance from the vehicle, a user may experience difficulty in operating the RKE fob to successfully perform various functions, such as locking or unlocking the vehicle.
Thus, there exists a need for an improved remote access device, such as an RKE fob, having an antenna that provides for low-frequency magnetic field transmission and/or reception in more than a single plane. Such a remote access device would preferably include an inductive coil antenna having two or three inductors oriented in multiple directions, such as along X and Y axes, or X, Y and Z axes, in order to optimize magnetic field transmission and/or reception in more than a single plane. Such a remote access device would thereby provide improved operation with respect to the orientation and/or distance problems described above, such as those associated with currently available RKE fobs.